1. Field of the Invention
The present invention generally relates to a surface acoustic wave device, a package for the device, and a method of fabricating the device.
2. Description of the Related Art
As electronic apparatuses with higher performances have become smaller in size, electronic devices to be mounted to such apparatuses are also expected to be smaller and have higher performances. Especially, surface acoustic wave (SAW) devices to be used as electronic parts such as filters, delay lines, and oscillators for electronic apparatuses that transmit or receive electric waves have been required to have downsized packages and high performance.
The conventional SAW device has a SAW chip, which is hermetically sealed in a cavity. The SAW chip has a piezoelectric substrate on which interdigital transducers (hereinafter referred to as IDT) having comb-like electrodes are formed. This type of the SAW device is described in, for example, Japanese Patent Application Publication 2001-176995. The IDT on the input side converts an electric signal applied thereto into a SAW, which propagates on the piezoelectric substrate. The IDT on the output side converts the received SAW into an electric signal that has been subjected to a given modulation.
A description will now be given of a conventional SAW device 100 with reference to FIGS. 1 and 2. FIG. 1 is a perspective view of the SAW device 100, and FIG. 2 is a sectional view taken along a line F-F shown in FIG. 1.
Referring to these figures, the SAW device 100 has a package 101 having a cavity 102 in which a SAW chip 120 is housed. Metal patterns, which include IDTs 122, interconnection lines 124, and electrode pads 123, are formed on a circuit-formed surface (main surface) of a piezoelectric substrate 121. The bottom surface of the cavity 102 (die-attached surface) is provided with metal patterns, which include electrode pads 109 aligned with the electrode pads 123 of the SAW chip 120. The SAW chip 120 is flip-chip bonded on the die-attached surface in the facedown state by using metal bumps 112. Thus, the package 101 and the SAW chip 120 can be electrically and mechanically connected to each other. The electrode pads on the die-attached surface are electrically connected to foot patterns 107 formed on the bottom surface of the package 101 (opposite to the surface defining the cavity 102) through interconnection lines and via interconnections 108. The cavity 102 is sealed with a resin 103.
However, the cavity 102 cannot be sealed with only the resin 103 with high reliability. The above sealing structure does not show good results in a test of measuring moisture resistance.